1. Field of the Invention
Embodiments of the disclosure relate in general to the field of computers and similar technologies, and in particular to software utilized in this field. Still more particularly, it relates to managing storage system resources in a storage area network (SAN).
2. Description of the Related Art
A storage area network (SAN) is an architecture for attaching remote computer storage devices, such as disk arrays, to servers in such a way that the storage devices appear as if they were locally attached to the server's operating system. SANs are typically implemented using Small Computer System Interface (SCSI) storage devices, which are used to create Logical Unit Numbers (LUNs), which are SCSI protocol entities that perform typical storage operations such as data reads and writes. A LUN typically corresponds to a storage volume and is represented within a computer operating system as a device. The use of a LUN is typically initiated by a SCSI initiator, such as an information processing system, which issues a reservation request for use of a LUN on a target data storage device. In response to the request, the target data storage device reserves the LUN for exclusive use by the SCSI initiator.
However, if the SCSI initiator (e.g., a host system) abnormally terminates or ends operation while the LUN is still reserved, then the reserved LUN, and its associated storage resources, may be inaccessible to other SCSI initiators. Current approaches to this issue include clearing SCSI-2 reservations on the target data storage device by issuing a LUN reset or a target reset command from a different initiator. In the case of a SCSI-3 reservation, a special command has to be sent from an initiator with a Persistent Reservation (PR) Key authorization. This approach requires explicit action from a SCSI initiator side to clear the reservation. However, when these approaches are employed, no other SCSI initiator can access a LUN until a hard reset or LUN reset is performed in the case of a SCSI-2 initiator, or a PREEMPT command is performed in the case of SCSI-3 initiator. Furthermore, if a SCSI initiator is abnormally terminated while holding a Persistent Reserve, then another SCSI initiator has to issue a PREEMPT and REGISTER command before it can access the LUN.